Uroptychus adiastaltus, Baba, 2018

Baba, Keiji, 2018, Chirostylidae of the Western and Central Pacific: Uroptychus and a new genus (Crustacea: Decapoda: Anomura), Tropical Deep-Sea Benthos (Mémoires du Muséum national d'Histoire naturelle 212), pp. 1-612 : 42-45

Uroptychus adiastaltus n. sp.

Figures 5 , 6

TYPE MATERIAL — Holotype: New Caledonia, Isle of Pines. BIOCAL Stn DW 33, 23°11’S, 167°10’E, 675-680 m, 29.VIII.1985, 1 ov. ♀ 4.3 mm ( MNHN-IU-2012-687 ) . Paratypes: New Caledonia, Isle of Pines. BIOCAL Stn DW33, 23°11’S, 167°10’E, 675-680 m, 29.VIII.1985, 3 ♂ 3.3-4.9 mm, 7 ov. ♀ 3.7-4.6 mm (MNHN-IU-2014-17157) . – Stn DW36, 23°09’S, 167°11’E, 650-680 m, 29.VIII.1985, 1 ♂ 2.8 mm, 2 ov. ♀ 3.5, 3.7 mm (MNHN-IU-2012-685) . – Stn DW51, 23°05’S, 167°45’E, 680- 700 m, 31.VIII.1985, 13 ♂ 2.3-3.1 mm, 12 ov. ♀ 2.7-3.6 mm, 5 ♀ 2.2-3.9 mm ( MNHN-IU-2012-684 ). MUSORSTOM 4 Stn DW220, 22°58.5’S, 167°38.3’E, 505-550 m, 29.IX.1985, 5 ♂ 3.3-3.7 mm, 2 ov. ♀ 3.5, 3.6 mm, 1 ♀ 3.1 mm ( MNHN- IU-2012-686). New Caledonia, Norfolk Ridge. NORFOLK 1 Stn DW1666, 23°42’S, 167°43’E, 469-860 m, 20.VI.2001, 1 ov. ♀ 4.9 mm (MNHN-IU-2012-693). NORFOLK 2 Stn DW2027, 23°26.34’S, 167°51.38’E, 465-650 m, 21.X.2003, 2 ♂ 4.9, 5.0 (MNHN-IU-2014-17158) . – Stn DW2091, 24°45,36’S, 168°06.24’E, 600-896 m, 29.X.2003, 1 ♂ 3.7 mm ( MNHN- IU-2012-690) . – Stn DW2101, 23°55.09’S, 167°44.10’S, 700-730 m, 30.X.2003, 1 ♀ 4.0 mm (MNHN-IU-2012-688) . – Stn DW2106, 23°53.72’S, 167°41.76’E, 685-757 m, 30.X.2003, 1 ov. ♀ 3.7 mm (MNHN-IU-2012-689).

ETYMOLOGY„ From the Greek adiastaltos (not clearly defined), alluding to sternite 3 medially bearing a poorly defined sinus, by which the species is readily distinguished from U. kareenae n. sp., U. depressus n. sp. and U. levicrustus Baba, 1988 .

DISTRIBUTION„ Isle of Pines and Norfolk Ridge, in 465- 896 m.

SIZE„ Males, 2.3-5.0 mm; females, 2.2-4.9 mm; ovigerous females from 2.7 mm.

DESCRIPTION — Small species. Carapace: Slightly broader than long (0.9 × as long as broad); greatest breadth 1.7-1.8 × distance between anterolateral spines. Dorsal surface feebly convex from anterior to posterior, without any distinct border; surface nearly smooth, sparingly with short fine setae. Lateral margins divergent posteriorly to point at anterior end of branchial region, then subparallel or slightly divergent posteriorly; ridged along branchial margin; anterolateral spine well developed, overreaching lateral orbital spine; branchial margin with well-developed spine at anterior end, followed by a few to several granulate ridges visible in lateral view, occasionally 1 or 2 very small spines. Rostrum narrow triangular, with interior angle of 22-24°, length usually slightly less than half, rarely about half that of carapace, breadth about one-third to two-fifths carapace breadth measured at posterior carapace margin; dorsal surface slightly concave. Pterygostomian flap anteriorly moderately angular, ending in distinct spine, smooth on surface.

Sternum: Excavated sternum broad triangular on anterior margin, with weak ridge in midline; sternal plastron slightly broader than long, lateral extremities divergent posteriorly. Sternite 3 well depressed, anterior margin of broad V-shape medially sharply notched, laterally angular. Sternite 4 having anterolateral margin relatively short, three-quarters as long as posterolateral margin, convex, anteriorly ending in blunt corner; anterolateral margin of sternite 5 convex, about half as long as posterolateral margin of sternite 4.

Abdomen: Smooth and nearly glabrous; somite 1 with antero-posteriorly convex transverse ridge. Somite 2 tergite 2.4-2.8 × longer than broad; pleural lateral margins feebly concave and weakly divergent posteriorly. Pleuron of somite 3 posterolaterally blunt angular. Telson half as long as broad or slightly less than so, feebly emarginate or slightly concave on posterior margin, posterior plate 1.2-1.4 × longer than anterior plate.

Eye: Relatively short (1.4 × longer than broad), reaching or slightly overreaching midlength of rostrum, medially somewhat swollen; cornea not inflated, more than half length of remaining eyestalk.

Antennule and antenna: Ultimate article of antennular peduncle 3.4 × longer than high. Antennal article 2 with small lateral spine; antennal scale reaching distal end of antennal article 5; article 4 usually unarmed, occasionally with tuberclelike mesial distoventral spine; article 5 unarmed, 1.4 × length of article 4, breadth about half height of ultimate article of antennule; flagellum of 9-12 segments far falling short of distal end of P1 merus. Mxp: Mxp1 with bases separated. Mxp3 basis without denticle on mesial ridge. Ischium with distally rounded flexor margin, no distinct denticle on crista dentata. Merus 2.1 × longer than ischium, flattish on mesial face, weakly ridged along flexor margin, distolateral spine obsolescent; flexor margin unarmed or with obsolescent spine somewhat distal to midlength; carpus with tiny distolateral spine.

Pereopods sparsely with soft fine setae.

P1: Slender, 5.5-6.0 × longer than carapace. Ischium dorsally with dorso-ventrally flattened, short spine, ventromesially with strong subterminal spine proximally followed by a few denticles. Merus 1.2-1.3 × longer than carapace, ventromesially with strong or moderate-sized spines: 1 at distal end, 1 at proximal end (these spines not prominent in small specimens), and occasionally additional few small spines between. Carpus 1.4-1.5 × longer than merus. Palm 3.5-4.3 × (males), 5.5- 5.7 × (females) longer than broad, subequal to or slightly shorter than carpus. Fingers slightly incurved distally, gaping in large males, not gaping in females and small males, movable finger 0.4-0.5 × length of palm; opposable margin of movable finger with obtuse process of triangular shape having proximal margin oblique; that of fixed finger with prominence or lower process distal to position of opposite process of movable finger.

P2-4: Meri flattish on mesial face, moderately inflated on lateral face, dorsal margin rounded, successively shorter posteriorly (P3 merus 0.9 × length of P2 merus, P4 merus 0.8-0.9 × length of P3 merus), subequally broad on 3 and P4, slightly narrower on P2, length-breadth ratio, 3.5-3.6 on P2, 2.9-3.1 on P3, 2.4-2.6 on P4; P2 merus 0.7-0.8 × length of carapace,1.0-1.2 × longer than P2 propodus; P3 merus about as long as P3 propodus; P4 merus 0.7-0.8 × length of P4 propodus. Carpi subequal, 0.4 × length of propodus on P2, 0.3 × on P3 and P4. Propodi usually subequal on P3 and P4, shorter on P2, rarely successively longer posteriorly; flexor margin straight, ending in pair of long movable spines preceded by 4, 3-4, 2-3 single spines at most on distal half of length on P2, P3, P4, respectively. Dactyli much longer than carpi (1.3-1.5 ×, 1.6-1.9 ×, 1.8-2.0 × longer on P2, P3, P4, respectively), distinctly more than half (0.6 × on P2 and P3, 0.6- 0.7 × on P4) as long as propodi, well compressed, relatively broad distally; flexor margin straight, with 16-20 (P2), 18-22 (P3-4) obliquely directed spines nearly contiguous to one another and obscured by setae, ultimate more slender than antepenultimate, penultimate more than 2 × broader than antepenultimate, remaining spines distinctly broader than ultimate spine except for proximal spines; antepenultimate spine 2.0-2.7 × longer than broad.

Eggs. Number of eggs carried, up to 12; size, 0.83 × 0.92 mm - 1.10 × 1.30 mm.

PARASITES„ One of the females from BIOCAL Stn DW51 (MNHN-IU-2012-684) bears a rhizocephalan externa on

the abdomen.

REMARKS„ Uroptychus adiastaltus keys out in a couplet together with U. alius Baba, 2005 (see above under the key to species), having the anteriormost branchial marginal spine not followed by distinct spines. However, the very characteristic sternite 4, having the anterolateral margin much shorter than the posterolateral margin, links U. adiastaltus much more closely to U. depressus n. sp., U. kareenae n. sp. and U. levicrustus Baba, 1988 . Their relationships are discussed under the remarks of U. kareenae .

Figures

FIGURE 5 Uroptychus adiastaltus n. sp., holotype, ovigerous female 4.3 mm (MNHN-IU-2012-687). A, carapace and anterior part of abdomen, dorsal. B, same, lateral. C, sternal plastron, with excavated sternum, basal parts of Mxp1 included. D, telson. E, left antenna, ventral. F, right Mxp3, ventral. G, same,lateral. Scale bars:1 mm.

FIGURE 6 Uroptychus adiastaltus n. sp.,holotype, ovigerous female 4.3 mm (MNHN-IU-2012-687).A, right P1, proximal part, dorsal.B, same,ventral.C, same, distal 3 articles,dorsal. D, same,fingers,ventral.E, left P2,lateral.F, same,distal part,setae omitted,lateral.G, left P3,setae omitted,lateral.H, same, distal part, lateral. I, left P4, lateral. J, same, distal part, lateral.Scale bars: 1 mm.